Separation of copper minerals from pyrite

ABSTRACT

A process of separating copper minerals from pyrite wherein a flotation concentrate containing copper minerals and pyrite is reground in the presence of lime and subsequently conditioned at a pH of 12.0 or more for a predetermined period sufficient to depress the pyrite, with optional additions of sulf-hydryl collector, cyanide and dispersing agent, and the conditioned pulp is subjected to flotation.

Enited Stat w Patent 11 1 Weston 1 1 SEPARATION OF COPPER MINERALS FROM PYRllTE [76] Inventor: David Weston, 34 Parkwood Ave.,

Toronto, Ontario, Canada 221 Filed: 1116627, 1973 211 App1.No.:374,1)24

Related 0.8. Application Data [63] Continuation of Ser. No. 115,709, Feb. 16, 1971,

abandoned.

[52] US. C1 241/20, 241/24, 209/3, 209/167 [511 1111i. C1 B0311) 1/04 [58] Field of Search 209/166, 167; 241/20, 24, 241/3 [56] References Cited UNITED STATES PATENTS 1,176,441 3/1916 Gayford 209/166 1,554,216 9/1925 Keller 1 209/167 X 1,554,220 9/1925 Leuis 209/167 1,837,852 12/1931 Christmann.... H 209/166 1,893,517 1/1933 Goudin 209/167 2,349,631 5/1944 Ruckwardt 209/167 1 Nov, 12, 1974 OTHER PUBLICATIONS Goudin, Flotation, MeGrawHi11, 1957, pgs. 430-433v Primary Examiner-Robert Halper 4 Attorney, Agent, or Firm-Depao1i & OBrie [57] ABSTRACT A process of separating copper minerals from pyrite wherein a flotation concentrate containing copper minerals and pyrite is reground in the presence of lime and subsequently conditioned at a pH of 12.0 or more for a predetermined period sufficient to depress the pyrite, with optional additions of sulf-hydryl collector, cyanide and dispersing agent, and the conditioned pulp is subjected to'flotation;

9 Claims, N0 Drawings This is a continuation, of application Ser. No. 115,709 now abandoned, filed Feb. 16, I971.

This invention relates to the separation of copper minerals-from pyrite.

Copper minerals frequently occur in association with pyrite. When such ores are concentrated by froth flotation the normal tendency is for the pyrite to report in the copperconcentrate. The presence of the-pyrite in the copper concentrate lowers the grade thereof and it has been the practice to attempt to eliminate as much as possible of the pyrite through the use of pyrite depressing agents during the rougher flotation.

Unfortunately the use of pyrite depressing agents such as cyanide during the rougher flotation has, in the past, been only partly effective and has succeeded to the extent that it has, only at the expense of lower recovery of the copper minerals. This has made necessary a compromise between pyrite elimination and copper recovery which results in" the presence of a considerable amountof pyrite in copperconcentrates delivered to the smelter. In the case of many ore bodies the principal sulphur containing ingredient in concentrates delivered to the smelter is pyrite. While pyrite may be tolerated in copper concentrates in the sense that such concentrates are capable of being smelted, its presence adds to the expense of the smelting operation both in terms of operatingcosts and in the capital 'costof smelter installation per pound of copper produced.

Perhaps more important than the economic disadvantages brought about' by the presence of pyrite in copper concentrates is the air pollution which resultsfrom the noxious gases, mainly sulphur dioxide, which are released during smelting. Consequently there has been,and is, considerable demand for a means of eliminating, to the maximum possible extent, the presence of pyrite in copper flotation concentrates.

GENERAL DESCRIPTION OF INVENTION 1 have discovered that it is possible to separate pyrite unit. The amount can vary in the range of '50 to500 percent per ton of feed to the regrind unit as compared to the amount of sulf-hydryl collector used per ton of feed in the rougher flotation circuit. Normally, I have found that in following my invention, lime alone may be used effectively asthe depressant for the pyrite, but only after the copper minerals together with the pyrite have been floated at least once to form a copper pyrite concentrate. In addition, if the ore contains an appreciable host rock slime content, a dispersant such as sodium silicate should be present in at least one stage of flotationin the production of the flotation concentrate.

from copper concentrates to a very effective extent I without significant losses of copper values. According to my invention a flotation concentrate is produced which contains the copper minerals and suchof the pyrite as will normally float therewith. Surprisingly, even though the pyrite may be essentially free of being combined with any of the copper minerals, with my invention it isnecessary to regrind, in a wet regrind mill, at least part of the copper pyrite concentrate. For instance, if the regrinding circuit is in closed circuit with a classifier, the concentrate may be fed first to the classifier, with the finely ground portion of the concentrate going directly from the classifier to the conditioning circuit and the coarse fraction going to the head of the regrind mill. Although this circuit may be used, l'generally prefer to feed all of the concentrate to the head of Where a rougher flotation concentrate is fed to the regrind circuit the dispersant will be added to a conditioning stage preferably ahead of the rougher flotation circuit. Where the flotation concentrate is either a concentrate produced from a first or second cleaner, the dispersant may be added either prior or during the rougher float, prior to the first cleaner float, or prior to the second cleaner float, in all three cases o'ralternately to onlyone or two points in the system such as in the conditioning stage before the first cleaner and in a conditioning stage prior to the second cleaner. The time of conditioning with a dispersant is normally a maximum of 3 minutes and in plant practice no specific conditioning equipment need be used other than, let us say, during the pumping time taken in pumping therougher concentrate to the first cleaner circuit. In this circuit,

in addition to the high pH required, the additionof a. sulf-hydryl collector to the grinding unit may be of major importance. Where I use cyanide in conjunction with lime as the pyrite depresssant, I have found it most important to add at least the majority of the cyanide in the conditioning stage following the regrind mill and just prior to the cleaner flotation circuit following the regrind circuit. If the bulk of the cyanide is added to the regrind mill itself, serious copper losses may ensue in the following cleaner flotation step or steps. I

Although in some conditions a single stage of conditioning and refloating after the regrind mill is satisfactory, Ihave found it preferable to use two stages of conditioning and two stages .of floating following the regrind mill. Where I use cyanide in conjunction with the lime, the optimum addition point of the cyanide is to either one or both of the conditioning steps ahead of.

the flotation circuits following the regrind mill.

I have found that the lime addition necessary to control the pH in the regrind circuit is of minor importance compared to the normally higher pH that is required in the one or two conditioning stages following the regrind circuit. If a single stage of conditioning is used the pH in the conditioning stage must be in excess of a pH of 12 and preferably in the range of 12.3 to 12.5. If two stages of conditioning are used the pH in the first conditioning stage may bebelow a pH of 12 with the second stage being at a pH in excess of 12 and preferably in the range of 12.3 to 12.5.

If the flotation concentrate fed to the regrind circuit is high in insol, comparatively'large amounts of dispersant may be used, such as sodium silicate, tetra-sodium pyrophosphate or the lignen family of dispersants.

quantities of the sulf-hydryl collector to the regrind Where such heavy concentrations of dispersant are used, for instance, in excess of 5 pounds of sodium silicate per ton of concentrate, lhave found it necessary to use comparatively large concentrations of sulfhydryl collector to prevent undue copper losses. In the EXAMPLES OF THE INVENTION The following examples are illustrative of the process of the invention:

Example I A composite sample of daily concentrator feed of a major copper producer in the United States had the following analysis:

Cu (Total) 1.09% Cu(Acid-Soluble) 0.36% Fe 7.55% S 3.23%

The sample was ground in the laboratory mill with the addition of 0.625 pounds per ton of soda ash to produce a pH of 7.55. The resulting pulp was conditioned for two minutes with 8.5 lbs. per ton of lime which produced a pH of 11.75. The pulp was then subjected to a second conditioning cycle for 19 minutes with 0.255 lbs. per ton of potassium amyl xanthate (Z6) added in stages. The pH at the end of the conditioning was 11.6. The pulpwas then subjected to a third conditioning cycle for 5 minutes with the addition of 6.25 lbs. per ton-of sodium silicate with 3 drops of pine oil for the last Z'minutes. The sodium silicate caused the pH to drop to 11.4. ll

The pulp was then subjected to flotation, the rougherfloat requiring 7 minutes with the addition of 0.025 lbs. per ton of Z6 and one drop of pine oil. Following the first cleaner the cleaner concentrate was filtered and reground with sufficient lime to produce a pH of 1215.

Following regrind the pulp was placed in a 250 gram Denver cell and conditioned with 1.25 lbs. of NaCN per ton of regrind feed and 7.7 lbs. perton of Na SiO In the third cleaner the pH was raised to 12.35-with lime and 1.9 lbs. of NaCN per ton of feed was added and the pulp was conditioned before floating.

The results were as follows:

Produce Wt. Analysis Cu cu Distribution Concentrate 2.5 35.7 83.5

No. 3 Clnr. Tlg. 2.7 2.1 5.3

No.2 Clnr. Tlg. 2.8 1.5 3.9

No. l Clnr. Tlg. 0.19 2.3

Rougher Tlg. 7 0.067 0 lll0.0 I 100.0

In the foregoing test the heavy activation brought aboutby the conditioning prior to the rougher float caused virtually all of the pyrite to report in the first dium silicate was used to reject the insol in the second cleaner tailing. Concentrations of cyanide in excess of one pound per ton were used which in a normal circuit would be considered impossible, as the copper losses would have been unacceptably high. It will further be noted that 9.2 percent of the total copper is in the second and third cleaner tailings. On the closed circuiting of these tailings the calculated recovery would be 80 or approximately 7 percent of the total copper, resulting in an overall recovery of slightly in excess of 90 percent of the original copper values and at a grade of concentrate of 35 percent. In the conventional circuit the grade of concentrate produced was approximately 16 percent copper at a recovery of less than 80 percent.

Example 11 Two samples of ore from an ore body in the Phillipines having a head assay of 0.64 percent total copper with the sulphide content consisting mainly of chalcopyrite and pyrite and wherein the copper minerals were mainly chalcopyrite with small amounts of copper oxide were ground in the laboratory rod mill and treated by procedures analogous to those of Example 1 to produce first cleaner concentrates which were then combined and reground for 3 minutes in a laboratory ball mill with 37 lbs. of lime per ton of concentrate. The resulting pulp was then refioated to produce a second cleaner concentrate having a grade of 24.4 percent copper containing 92.3 percent of the total copper compared to the combined first cleaner concentrates which contained 95.8 percent of the total copper at a grade of 18.4 percent.

As it is estimated that 80 percent of the copper in the No. 2 cleaner tailings would be recovered in closed circuiting, the recovery at the grade of 24percent copper would'be approximately 95 percent. It will be noted that with the extremely high amount of lime used to the regrind circuit to produce an end pH in excess of 12, the grade of copper was increased by approximately 32 percent with but a minor drop in copper values. Furthermore, with the large amount of lime addition to the regrind mill resulting in a final pl-lfror'n the regrind mill in excess of-12, it was not necessary to add any further lime ahead of the second cleaner float.

Example '111 Two further samples of the same ore as that used in Example 11 were treated in a manner analogous to the procedure of Example 1 to produce first cleaner concentrates which were then'combined to produce a combined concentrate analyzing 16.7 percent copper and containing 95.6 percent of the total copper. The con-. centrate was reground in the laboratory rod mill for 3 minutes with 41 lbs. of lime per ton of concentrate and the resulting pulp was conditioned and refloated to produce a second cleaner concentrate having a grade of 25.2 percent copper and containing 91.7 percent of the total copper.

Example 1V Two further samples of the same ore as that used in.

Examples 11 and 111 were treated in an analogous man-,

ner to produce first cleaner concentrates which were resulting pulp was conditioned with additional lime to bring the pH up to 12.5 for 8 minutes and floated to produce a cleaner concentrate having a grade of 27.3 percent copper and containing 91.8 percent of the total copper.

In comparing this example with the previous example it will be noted that with the higher concentration of lime bringing the pH up fromaround 12.1 to 12.5, the concentrate grade was appreciably increased with no further drop in copper values.

Example V The combined first cleaner concentrate produced from two further samples of the same ore as that used in Examples ll, ill and 1V analyzed 17.4- percent (In and contained 95.9 percent of the total copper. The combined cleaner concentrate was reground in thelaboratory ball mill with 41 lbs. of lime per ton and one pound of potassium amyl xanthate (Z6) per ton of feed. The resulting pulp was conditioned for 8 minutes and refloated to produce a second cleaner concentrate, and this concentrate conditioned at pH of 12.5 with CaO to produce the third and final cleaner concentrate analyzing 28.4 percent Cu and containing 92.2 percent of the total copper values.

in comparing this test with Example lV it will be noted that with the addition of the sulf-hydryl collector to the regrind mill, and using two stages of conditioning and cleaning the final concentrate grade was not only higher, but also resulted in higher overall recovery of the copper values in the open circuit.

In either using lime alone as the pyrite depressant or lime in conjunction with cyanide, l have found that the minimum conditioning period required for satisfactory pyrite depression is 2 minutes in at least one conditioning stage. Further, with so-called clean ores, that is, that produce a minimum amount of slimes, a rougher concentrate is satisfactory as the feed to the regrind mill. However, with rougher concentrates that contain comparatively large amounts of host rock slime I prefer to clean the rougher concentrate at least once, preconditioning the rougher concentrate with a dispersant 11. A process for the separation of copper values from copper ores containing pyrite by differentiai flotation comprising; preparing a copper-pyrite flotation con centrate which is substantially free of slime host rock materials; grinding said copper-pyrite flotation concentrate in the presence of calcium hydroxide; agitation conditioning the thus produced pulp at a pH of at least 12.3 in the presence of a sulf-hydryl collecting agent for a period of time sufficient to depress the pyrite; and then subjecting the resulting pulp to flotation in the presence of a suitable frother to produce a copper concentrate enriched in copper values and impoverished in pyrite, and a tailings impoverished in copper values and enriched in pyrite.

2. A process as defined in claim ll wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf hydryl collector already used to produce said flotation concentrate.

3. A process as defined in claim 11 wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf-hydryl collector is added at a rate, per ton of said gringing feed, equal to at least 50 percent of the rate, per ton of original feed of sulfhydryl collector already used to produce said flotation concentrate and cyanide is added during said agitation conditioning.

1'. A process as defined in claim l wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulfhydryl collector already used to produce said flotation concentrate and cyanide is added at a rate equivalent such as sodium silicate or lignen sulphonate or one of a the family of phosphates prior to reiloating to produce a first cleaner concentrate which under such conditions would be the feed to the regrind circuit.

Where i use the term regrind throughout this patent application, I am referring to a fine grinding wet ball mill circuit as distinguished from the primary and- /or secondary grinding which normally takes place prior to rougher flotation.

Where I used the term cyanide as an added pyrite depressant l am referring to the common commercial salts of cyanide normally used in plant practice such as sodium cyanide, potassium cyanide and calcium cyanide.

The term sulf-hydryl collector when used herein is intended to refer to that class of collectors having an SH group and typified by the xanthates as classified in Flotation", A. M Gaudin, McGraw Book Company, lnc., Toronto, 1957, p. 182.

What I claim as my invention is:

to at least one pound of sodium cyanide per ton of grinding feed.

5. A process as defined in claim 1 wherein said concentrate is a cleaner coppenpyrite concentrate derived from a flotation concentrate which has been refloated at least once in the presence of a dispersing agent.

ii. A process as defined in claim 11 wherein a sulfhydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf'hydryl collector already used to produce said copper-pyrite flotation concentrate.

7. A process as defined in claim l wherein a sulfhydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already added during rougher flotation and a dispersant is added dur ing conditioning of the thus produced pulp.

d. A process as defined in claim ll wherein a sulf hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said flotation concentrate and cyanide is added during said agitation conditioning stages.

9. A process as defined in claim 1 wherein the sulfhydryl collector is added during said grinding said copper-pyrite flotation concentrate. 

1. A PROCESS FOR THE SEPARATION OF COPPER VALUES FROM COPPER ORES CONTAINING PYRITE BY DIFFERENTIAL FLOTATION COMPRISING; PREPARING A COPPER-PYRITE FLOTATION CONCENTRATE WHICH IS SUBSTANTIALLY FREE OF SLIME HOST ROCK MATERIALS; GRINDING SAID COPPER-PYRITE FLOTATION CONCENTRATE IN THE PRESENCE OF CALCIUM HYDROXIDE; AGITATION CONDITIONING THE THUS PRODUCED PULP AT A PH OF AT LEAST 12.3 IN THE PRESENCE OF A SULF-HYDRYL COLLECTING AGENT FOR A PERIOD OF TIME SUFFICIENT TO DEPRESS THE PYRITE; AND THEN SUBJECTING THE RESULTING PULP TO FLOTATION IN THE PRESENCE OF A SUITABLE FROTHER TO PRODUCE A COPPER CONCENTRATE ENRICHED IN COPPER VALUES AND IMPOVERISHED IN PYRITE, AND A TAILINGS IMPOVERISHED IN COPPER VALUES AND ENRICHED IN PYRITE.
 2. A process as defined in claim 1 wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said flotation concentrate.
 3. A process as defined in claim 1 wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf-hydryl collector is added at a rate, per ton of said gringing feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said flotation concentrate and cyanide is added during said agitation conditioning.
 4. A process as defined in claim 1 wherein during said agitation conditioning of the thus produced pulp at a pH of at least 12.3, the sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said flotation concentrate and cyanide is added at a rate equivalent to at least one pound of sodium cyanide per ton Of grinding feed.
 5. A process as defined in claim 1 wherein said concentrate is a cleaner copper-pyrite concentrate derived from a flotation concentrate which has been refloated at least once in the presence of a dispersing agent.
 6. A process as defined in claim 1 wherein a sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said copper-pyrite flotation concentrate.
 7. A process as defined in claim 1 wherein a sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already added during rougher flotation and a dispersant is added during conditioning of the thus produced pulp.
 8. A process as defined in claim 1 wherein a sulf-hydryl collector is added at a rate, per ton of said grinding feed, equal to at least 50 percent of the rate, per ton of original feed of sulf-hydryl collector already used to produce said flotation concentrate and cyanide is added during said agitation conditioning stages.
 9. A process as defined in claim 1 wherein the sulf-hydryl collector is added during said grinding said copper-pyrite flotation concentrate. 